1. Field of the Invention
The present invention relates generally to a head positioning control system for a disk drive. More particularly, the invention relates to a head positioning control method in a disk drive using a sliding type actuator.
2. Description of the Related Art
Conventionally, in a disk drive, a head is shifted to follow a track on a disk medium surface by means of a head positioning control system employing a phase compensator, such as a read lag filter or a PID (feedback) compensator and so forth.
Particularly, in case of a floppy disk drive, since it is required to fix a disk medium on a spindle, a primary rotation synchronization run-out due to chucking error and a secondary rotation synchronization run-out due to expansion and contraction of a film medium should particularly cause problems. However, in the conventional floppy disk drive, positioning at high precision is not required, and positioning employing a stepping motor is sufficient.
On the other hand, in case of a large capacity floppy disk drive in the recent years, positioning at precision in the order of several xcexcm which is higher than that required for the conventional floppy disk drive, is required. Therefore, a method for obtaining a position error of the head from the disk medium surface with employing a VCM (Voice Coil Motor) as a motor.
A compression ratio relative to a low order spindle rotation synchronization frequency of run-out determined from a necessary head positioning precision is certainly obtained by taking a sufficient control band in a closed loop system employing a phase compensator.
On the other hand, in case of the hard disk drive, there has been proposed a method employing a frequency shaping filter improving a compression ratio characteristics of a frequency of rotation synchronization component as a loop characteristics by utilizing an internal principle as a rotation synchronous run-out filter in the hard disk drive and increasing a gain of a rotation synchronization component including a sine wave model within the closed loop. This method has been disclosed in xe2x80x9cAdvanced Methods for Repeatable Runout Compensationxe2x80x9d (IEEE Transactions on Magnetics, Vol. 31, No. Mar. 2, 1995).
In the positioning method of the head in the conventional disk drive set forth above, in case of the large capacity floppy disk drive, if greater capacity is sought, it becomes difficult to certainly provide compression ratio of the low order spindle rotation synchronous frequency of the run-out due to narrowing of a traffic pitch. Particularly, when a sliding type actuator is used, influence to non-linear friction between the movable portion and a guide rod is becoming significant.
On the other hand, in case of the method employing the frequency shaping filter in the hard disk drive, a memory for storing position error information for one turn becomes necessary to be a cause of cost-up.
The present invention has been worked out in order to solve the problems set forth above. It is therefore an object of the present invention to provide a head position control system for a disk drive which can reduce influence of static friction of a sliding type actuator which otherwise serves for degradation of low order spindle rotation synchronization run-out.
In order to accomplish the above-mentioned and other objects, according to one aspect of the present invention, a positioning control system for a disk drive comprises:
position error detecting means for detecting a position error between a center of a data track on a disk medium and a head for reading data from the disk medium;
shifting means for shifting the head;
a phase compensator for positioning the head at a target position on the basis of a result of detection of the position error detecting means;
detecting means for detecting influence of a static frictional force for the shifting means based on an output of the phase compensator;
a friction compensator outputting a feed forward signal for driving the shifting means; and
means for applying the feed forward signal from the friction compensator to the shifting means from the friction compensator when influence of the static frictional force to the shifting means is detected by the detecting means.
In the preferred construction, the shifting means may be a sliding type actuator. The friction compensator may detect influence of the static frictional force to the shifting means by monitoring at least one of a control signal for the shifting means output from the phase compensator or a driven current signal for driving the shifting means.
The feed forward signal may be a signal for generating a sufficient force for shifting the head against influence of static frictional force on the shifting means. The feed forward signal may be a peak value of one of the control signal and the drive current signal. The detecting means may detect influence of the static frictional force on the shifting means by monitoring result of detection of the position error detecting means.
Preferably, means for applying the feed forward signal to the shifting means may be a switch for switching between an output of the phase compensator and the feed forward signal from the friction compensator.
Namely, the positioning control system according to the present invention monitors drive signal for the actuator to make judgment that the static frictional force influences if the drive signal does not fall within the given range, for storing the peak value thereupon to generate the control signal generating the necessary force for shifting the movable portion. The stored peak value is then applied as the feed forward value for the next cycle to shift the movable portion which cannot be moved due to presence of the static frictional force otherwise.
As set forth above, by addition of the simple device, static friction of the sliding type actuator to be a cause of degradation of low order spindle rotation synchronization run-out can be reduced.